1. Field of the Invention
The invention relates generally to a safety coupling for a conduit, such as a hose of a vehicle extraction system, and more particularly to a safety coupling providing reliable operation and easy reconnect.
2. Description of the Related Art
Many industries use conduits for the transportation of liquids, gases, electric power, signals, data, and the like, over shorter or longer distances. The conduit may be a pipe, a hose, a cable, or any other conduit suitable for transporting the commodity of interest.
Such conduits are generally designed to withstand adverse conditions as may be encountered in the environment in which the conduit is located. However, conduits may occasionally encounter forces that are greater than the design specifications of the conduit allow for. Such unusual forces may be the result of, for example, an equipment failure, extreme weather conditions, or human error.
For these reasons, it must be anticipated that any conduit may encounter conditions that are so severe that the conduit will fail, for example rupture or break. It is desirable to provide a conduit with one or more safety couplings. The purpose of a safety coupling generally is to disconnect two ends of the conduit in case of an unusually strong force being exerted on the conduit. The operation of the safety coupling ensures that the conduit ends are disconnected before damage of the conduit occurs. An additional advantage of the use of a safety coupling is that disruption of the conduit takes place at a predictable location, making it easier to locate the interruption in the line. Safety couplings can be provided in places that are readily accessible, making repairs less cumbersome than they otherwise might be. For conduits that transport dangerous commodities, such as combustible or explosive materials, or high voltage electric power, the safety coupling can be combined with a shut off valve or a switch to prevent danger to the environment and personnel in the vicinity of the rupture.
These principles will be further illustrated with reference to vehicle exhaust extraction systems. Vehicle exhaust extraction systems are designed to permit indoor operation of internal combustion engines. These systems generally comprise a nozzle, which is designed to connect to the tailpipe of a vehicle; a flexible hose connecting the nozzle to an exhaust mechanism comprising a blower fan. The exhaust mechanism is in fluid communication with the outside air, so that the blower fan expels exhaust fumes to the outside via the flexible hose.
Many vehicle exhaust extraction systems are used with emergency vehicles, such as Emergency Medical Services (EMS) vehicles and fire trucks. It is desirable that the vehicle exhaust extraction system automatically disconnects from the tailpipe of the vehicle as the vehicle leaves the building in which it was parked. Since these vehicles need to respond to emergency calls, it is undesirable to use a system that requires manual intervention.
Nozzle systems have been developed that are designed to automatically disconnect from the tailpipe as the vehicle passes a predetermined point, or when the vehicle exerts a pulling force on the flexible hose exceeding a predetermined threshold value.
One type of system uses an inflatable cuff that fits around the exhaust pipe of the vehicle, or around an adapter fitted to the exhaust pipe of the vehicle. The cuff is connected to a control mechanism in such a way that the cuff deflates when the vehicle passes a predetermined point, for example when the rear of the vehicle passes the door opening of the building.
Another type of system uses electromagnets for attaching the nozzle to the tailpipe, or to an adapter fitted to the tailpipe. A control mechanism switches off the power to the electromagnets as the vehicle passes a predetermined point, cause release of the nozzle from the vehicle.
Yet another approach relies on permanent magnets for attaching the nozzle to the vehicle. The magnetic force is such that the nozzle remains securely connected to the vehicle during normal operation inside the building. The magnetic force is, however, small enough for the nozzle to disconnect from the vehicle as soon as the vehicle exerts an appreciable pulling force on the hose of the exhaust extraction system.
Although the automatic nozzles available in the market in general operate reliably, occasionally the nozzle does not disconnect as intended, or the nozzle or another part of the exhaust extraction system gets caught behind a protrusion of the moving vehicle. Such mishaps can cause serious damage to the vehicle, to the exhaust extraction system, or both. To prevent such damage, exhaust extraction systems generally comprise a safety coupling designed to disconnect in case the nozzle release mechanism fails, or when the exhaust extraction system remains attached to the vehicle for some other reason.
DE 196 22 860 discloses a safety coupling comprising two external hose coupling parts for coupling together two hose ends. Inside the hose coupling parts are mounted mating portions of a wire coupling, connected to the nozzle and to the hose trolley, respectively. If the nozzle fails to disengage a pulling force is exerted on the wire. If the pulling force exceeds a predetermined threshold value the wire coupling disengages. As this safety coupling relies on a mechanical trigger for disengagement, it is itself subject to occasional malfunction. Moreover, the mechanism is relatively complicated, requiring fine-tuning in order for it to operate properly.
US Patent Application Publication 2004/0075273 discloses a safety coupling designed as a tubular, two-part flange, one flange having a straight edge, the other flange having a conical edge. The two flanges are held together by a resilient locking ring, which is comprised of a number of segments. The segments are held together by spring-loaded bolts. The coupling disconnects when a pulling force is exerted on the flanges large enough to overcome the spring bias of the ring, so that the ring segments are pushed apart.
WO 2008/088272 discloses a coupling system comprising a coupling member and an actuating member. The coupling member is operated pneumatically. Disconnection is triggered by the actuating member. The mechanism is mounted inside the duct for exhaust gas extraction, which exposes the mechanism to the corrosive components of exhaust gases. As the system relies on a mechanical trigger mechanism, it is subject to potential malfunction.
Thus, there is a particular need for a safety coupling that does not comprise a separate actuation mechanism.
There is a further need for a safety coupling having a factory set release force, and does not require adjustment by the end user.
There is a further need for a safety coupling that can be re-connected easily.